Conventional commutation device adapted into three-phase brushless DC (direct current) motor is configured for obtaining dynamic positions of rotor of the motor according to counter electro-dynamic potential of three-phase excitation coil of the motor and neutral-point voltage of the three-phase excitation coil, to further provide corresponding excitation current to the three-phase excitation coil, such that the motor continuously operate. However, zero-crossing detection circuit of the conventional commutation device is very complex in the circuit design, and the size thereof is very large, which will be described in FIG. 1.
FIG. 1 is a circuit view of a conventional zero-crossing detection circuit. As shown in FIG. 1, the circuit structure as marked by labels 19 and 21 comprises three same circuits, and all of the three same circuits need to use the neutral-point voltage of the three-phase excitation coil (that is, the voltage of the node N). In addition, from FIG. 1 it can be seen that, each of coils of the three-phase excitation coil needs to cooperate with a corresponding one of the three same circuits to operate.
From the above description it can be seen that, the conventional zero-crossing detection circuit is very complex in design, such that the size thereof is very large.